diff --git a/README.md b/README.md
index f2dd4fa..f5233a9 100644
--- a/README.md
+++ b/README.md
@@ -154,6 +154,28 @@ echo "Total: $(($price * $TAX))"
 ~~~
 ```
 
+If you add a `choices` list, `mask` will validate if the flag value is one of them.
+
+**Example:**
+
+`````markdown
+## print (text)
+
+> Print text with color
+
+**OPTIONS**
+* color
+    * flags: -c --color
+    * type: string
+    * choices: RED, BLUE, GREEN
+    * desc: Color of the text.
+
+```sh
+COLOR=${color:RED} # Fallback to RED if not supplied
+echo "$COLOR: $text"
+```
+`````
+
 If you exclude the `type` field, `mask` will treat it as a `boolean` flag. If the flag is passed, its environment variable will be `"true"`, otherwise it will be unset/non-existent.
 
 Important to note that `mask` auto injects a very common `boolean` flag called `verbose` into every single command even if it's not used, which saves a bit of typing for you. This means every command implicitly has a `-v` and `--verbose` flag already.
diff --git a/mask-parser/src/maskfile.rs b/mask-parser/src/maskfile.rs
index 5a0c541..c5f0f28 100644
--- a/mask-parser/src/maskfile.rs
+++ b/mask-parser/src/maskfile.rs
@@ -57,6 +57,7 @@ impl Command {
                 takes_value: false,
                 required: false,
                 validate_as_number: false,
+                choices: vec![],
                 val: "".to_string(),
             });
         }
@@ -107,6 +108,7 @@ pub struct NamedFlag {
     pub multiple: bool,           // Can it have multiple values? (-vvv OR -i one -i two)
     pub takes_value: bool,        // Does it take a value? (-i value)
     pub validate_as_number: bool, // Should we validate it as a number?
+    pub choices: Vec<String>,     // Choices of flag value.
     pub required: bool,
     /// Used within mask. TODO: store in a different place within mask instead of here.
     #[serde(skip)]
@@ -124,6 +126,7 @@ impl NamedFlag {
             takes_value: false,
             required: false,
             validate_as_number: false,
+            choices: vec![],
             val: "".to_string(),
         }
     }
diff --git a/mask-parser/src/parser.rs b/mask-parser/src/parser.rs
index 38d687e..9971f2d 100644
--- a/mask-parser/src/parser.rs
+++ b/mask-parser/src/parser.rs
@@ -135,6 +135,12 @@ pub fn parse(maskfile_contents: String) -> Maskfile {
                                 }
                             }
                         }
+                        "choices" => {
+                            current_option_flag.choices = val
+                                .split(',')
+                                .map(|choice| choice.trim().to_owned())
+                                .collect();
+                        }
                         "required" => {
                             current_option_flag.required = true;
                         }
@@ -299,6 +305,7 @@ mod parse {
             "takes_value": false,
             "required": false,
             "validate_as_number": false,
+            "choices": [],
         });
 
         assert_eq!(
diff --git a/mask/src/main.rs b/mask/src/main.rs
index 39571d7..cb6f6ea 100644
--- a/mask/src/main.rs
+++ b/mask/src/main.rs
@@ -184,6 +184,18 @@ fn get_command_options(mut cmd: Command, matches: &ArgMatches) -> Command {
                 .unwrap()
                 .to_string();
 
+            if !flag.choices.is_empty() {
+                if !flag.choices.iter().any(|choice| choice == &raw_value) {
+                    eprintln!(
+                        "{} flag `{}` expects one of {:?}",
+                        "ERROR:".red(),
+                        flag.name,
+                        flag.choices,
+                    );
+                    std::process::exit(1);
+                }
+            }
+
             if flag.validate_as_number && raw_value != "" {
                 // Try converting to an integer or float to validate it
                 if raw_value.parse::<isize>().is_err() && raw_value.parse::<f32>().is_err() {
diff --git a/mask/tests/arguments_and_flags_test.rs b/mask/tests/arguments_and_flags_test.rs
index 53970f7..d3bbb74 100644
--- a/mask/tests/arguments_and_flags_test.rs
+++ b/mask/tests/arguments_and_flags_test.rs
@@ -177,6 +177,76 @@ Write-Output $sum
     }
 }
 
+mod choices {
+    use super::*;
+
+    #[test]
+    fn properly_validates_flag_with_choices() {
+        let (_temp, maskfile_path) = common::maskfile(
+            r#"
+## color
+
+**OPTIONS**
+* val
+    * flags: --val
+    * type: string
+    * choices: RED, BLUE, GREEN
+
+```bash
+echo "Value: $val"
+```
+
+```powershell
+param (
+    $in = $env:val
+)
+Write-Output "Value: $in"
+```
+"#,
+        );
+
+        common::run_mask(&maskfile_path)
+            .cli("color --val RED")
+            .assert()
+            .stdout(contains("Value: RED"))
+            .success();
+    }
+
+    #[test]
+    fn out_of_choices() {
+        let (_temp, maskfile_path) = common::maskfile(
+            r#"
+## color
+
+**OPTIONS**
+* val
+    * flags: --val
+    * type: string
+    * choices: RED, BLUE, GREEN
+
+```bash
+echo "Value: $val"
+```
+
+```powershell
+param (
+    $in = $env:val
+)
+Write-Output "Value: $in"
+```
+"#,
+        );
+
+        common::run_mask(&maskfile_path)
+            .cli("color --val YELLOW")
+            .assert()
+            .stderr(contains(
+                "flag `val` expects one of [\"RED\", \"BLUE\", \"GREEN\"]",
+            ))
+            .failure();
+    }
+}
+
 mod numerical_option_flag {
     use super::*;
 
diff --git a/mask/tests/introspect_test.rs b/mask/tests/introspect_test.rs
index 8e8c0ff..7c2a88f 100644
--- a/mask/tests/introspect_test.rs
+++ b/mask/tests/introspect_test.rs
@@ -27,6 +27,7 @@ echo something
         "takes_value": false,
         "required": false,
         "validate_as_number": false,
+        "choices": [],
     });
 
     let expected_json = json!({